Circuit breakers may be used to protect an electrical circuit coupled to an electrical power supply. Circuit breakers may automatically interrupt power to the electrical circuit when, e.g., an overcurrent (i.e., excessive current) is detected. An overcurrent may result from, e.g., a short circuit, an overload, or a ground fault. The automatic interruption of power may prevent electrical shock hazards and/or damage to electrical equipment and surrounding infrastructure. Circuit breakers may also be manually operated to connect and disconnect power to an electrical circuit by moving an operating handle mounted on the housing of the circuit breaker. The operating handle typically has three positions: ON, OFF, and TRIPPED. The ON position typically indicates that the main contacts of the circuit breaker are closed (i.e., in contact with each other), which connects power to the electrical circuit. The OFF position typically indicates that the main contacts have been opened manually via the operating handle to disconnect power from the electrical circuit. And the TRIPPED position typically indicates that the main contacts have been opened automatically by a tripping mechanism of the circuit breaker in response to detection of an overcurrent to also disconnect power from the electrical circuit.
Under some abnormal operating conditions, the main contacts may become welded, fused, or otherwise stuck together. For example, a high in-rush current and/or a partial failure and/or delay of the tripping mechanism may cause the main contacts to overheat to a point where they may fuse or weld together upon contact. Such a condition may go undetected. Consequently, a subsequent movement of the operating handle into the OFF position, which may not result in the stuck main contacts opening, may erroneously and dangerously indicate that power is disconnected from an electrical circuit when, in fact, power remains connected.
Accordingly, there is a need for apparatus and methods that prevent an operating handle of a circuit breaker from being moved into an OFF position after the main contacts of the circuit breaker have become stuck together. Such apparatus and methods may be referred to as “positive-off stop” apparatus and methods.